It is known to provide control systems to control the supply of fuel and air to furnaces, such as the type of furnace which is part of a boiler for a power plant. Such power plants normally have multiple burner assemblies in a windbox, the windbox being fed by a fan which may be controlled by, for instance, a variable speed motor or control damper. The windbox acts as a plenum to supply combustion air to a group of burner assemblies at the same time.
Conventional burner assemblies, such as that shown in U. S. Pat. No. 2,210,428 to Peabody, have been difficult to control. Such burner assemblies have registers which typically have had a shutter-like arrangement for controlling air flow, which shutter-like arrangement is located near the burner register discharge outlet immediately adjacent the throat of the furnace. These registers receive air from all sides and thus do not organize the air into a discrete stream in which total air flow may be measured. Moreover, the shutter-like air valves near the furnace throat, being subject to a very hostile environment involving high heat and combustion products, tend to become jammed and unusable. As such, they are typically left wide open by the furnace operator to avoid the problem of the shutter becoming stuck in an unduly restricted position. This, of course, has further reduced the opportunities for control of individual burner assemblies. Additionally, difficulties in measuring individual burner fuel flow increase the problems associated with control of the individual burner assemblies.
These problems with conventional burner assemblies have been resolved by the invention disclosed in U. S. Pat. No. 4,504,216 issued Mar. 12, 1985, to the present inventor, Donald K. Hagar, and to another co-inventor, Lyle D. Geiger, which patent is hereby incorporated herein by reference. In that patent, the burner assembly includes an air register surrounding the central fuel nozzle, which air register has an inwardly spiraling scroll passageway and a simple air control valve located upstream of the scroll passageway. With that invention, the combustion air is organized into a discrete flow path represented by the inwardly spiraling scroll passageway. This enables accurate measurement and control of the air flow. This control is enhanced by the simple upstream valve at the inlet to the scroll passageway, which valve is remote from the harsh environment at the outlet of the burner assembly. This simple valve is capable of controlling the entire air flow through any given burner assembly.
The present invention goes beyond the burner assembly itself, and provides an overall method and system in which the enhanced control capabilities offered by the burner assemblies of U.S. Pat. No. 4,504,216 become more fully realized through an overall method and arrangement which provides for optimum performance from a set of burner assemblies firing in unison.